In electrophotographic printing machines, toner particles are transferred to a printing medium by an inking device. After the toner has been transferred onto the printing medium, the toner is fused onto the printing medium. In many electrophotographic printing machines, fusing is done inside a fuser mechanism by heat and pressure.
In U.S. Pat. No. 5,536,921, a microwave fuser mechanism is shown as being used for fusing toner. For this purpose, the travel path of the printing medium runs through the microwave fuser mechanism, whereby the toner and the printing medium are heated and the toner is thus fused onto the printing medium.
It is also conceivable that microwave mechanisms be used for the situation where, for example, a fuser mechanism with a fuser roller and a pressure drum is used. In such case, the microwave mechanism can, for example, preheat the printing medium and the toner so that fusing takes less time.
If a printing medium is conveyed through a microwave mechanism on a conveyor belt, the conveyor belt must be subjected to heightened requirements. The belt must absorb very little micro-radiation and have the least possible effect upon the microwave field. In addition, it must not conduct electricity.
Problems can arise even if a suitable conveyor belt that does not conduct electricity is used, in particular, when layers of toner are on both sides of the printing medium. This is the situation in duplex printing. The quality of the printed image can be adversely affected by direct contact of the layer of toner that is on the bottom of the printing medium with the conveyor belt.
An additional problem that arises during the fuser process performed by a microwave fuser mechanism or, in general, during handling of a printing medium inside a microwave mechanism, is the water vapor escaping from the printing medium. This water vapor can spread out inside the microwave mechanism. The conductivity of the gaseous mixture present inside the microwave mechanism increases when this happens. Consequently, arcing can occur inside the microwave mechanism. Such arcing can cause damage inside the microwave mechanism.
In addition, moisture can condense on the walls inside the microwave mechanism or on other components in the immediate vicinity. This can at least cause the microwave field to be distorted. An interruption of or in the operation of the microwave mechanism is at the least, likely.